This invention relates to corrosion protection systems for corrodible storage vessels and in particular is directed to external and internal corrosion protection systems. Steel storage tanks and particularly buried steel storage tanks for containing liquid products such as petroleum products, are subject to a corrosive environment of the surrounding soil as well as internal corrosion due to the presence of a corrosive liquid within the tank or water within the tank. Therefore, buried steel storage tanks are subject to both external and internal corrosion.
It is known to provide sacrificial electrodes externally of the tank and connected thereto, with the surrounding soil environment completing the circuit between the sacrificial electrodes and the tank. Such sacrificial electrodes slowly corrode in preference to any exposed steel surface of the tank. Such external sacrificial electrodes do not protect the interior surface of the tank from corrosion. Therefore, existing external sacrificial electrodes only protect exposed exterior surfaces which otherwise would corrode.